Method of fabricating a reflection type liquid crystal display in which the surface of a substrate is roughened, a metal film is formed on the roughened surface, and a non-polarizing, transparent dielectric film is form on the metal film

ABSTRACT

There is provided a reflection type liquid crystal display including (a) a first substrate having a roughened surface, (b) a second substrate spaced away from the first substrate in opposing relation to the roughened surface of the first substrate, (c) a liquid crystal layer sandwiched between the first and second substrates, (d) a metal film formed on the roughened surface of the first substrate for reflecting lights therefrom, (e) a transparent dielectric film formed on the metal film, the transparent dielectric film having a planarized upper surface, (f) a plurality of transparent pixel electrodes formed on the transparent dielectric film, and (g) a plurality of switching devices formed on the transparent dielectric film, each of the switching devices being electrically connected with each of the transparent pixel electrodes, the transparent pixel electrodes and the switching devices being arranged in a matrix. The above-mentioned reflection type liquid crystal display makes it possible to provide an excellent light diffusion and reflection function without special technique. In particular, it is possible to reduce the number of photolithography steps for fabricating an active matrix type substrate, ensuring lower fabrication costs and a higher fabrication yield.

This is a divisional of application Ser. No. 08/964,990 filed Nov. 5,1997, the disclosure of which is incorporated herein by reference

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a liquid crystal display, and more particularlyto a reflection type liquid crystal display including an active matrixtype display having a thin film transistor as a switching device, and apassive matrix type without a switching device. The invention alsorelates to a method of fabricating such a reflection type liquid crystaldisplay.

2. Description of the Related Art

In recent years, a liquid crystal display has been widely used for apocket-type TV set and terminal devices for communication by virtue ofits small thickness and light weight. A reflection type liquid crystaldisplay without necessity of using a back light is in particular indemand because it is ultra-thin and light-weight, and it cansignificantly reduce power consumption. However, even if a back light isremoved out of a presently available transmission type color liquidcrystal display and a light reflection plate is added to a lower surfaceof the display, it would cause a problem that an efficiency of utilizinglights is low, and it is not possible to have practical brightness.

As a solution to this problem, there have been suggested variousreflection type liquid crystal displays for enhancing an efficiency ofutilizing lights. For instance, a certain reflection type liquid crystaldisplay is designed to include a pixel electrode having reflectionfunction, and another is designed to include no polarizing plates.

For another instance, a reflection type liquid crystal display suggestedin "Bright Reflective Multicolor LCDs addressed by a-Si TFTs" by S.Mitsui et al., Society for Information Display '92 Digest, pp. 437-440,is of a type where guest-host type liquid crystal including dichroismpigment is used as raw material for liquid crystal. FIG. 1 illustrates astructure of the suggested reflection type liquid crystal display.

The illustrated reflection type liquid crystal display includes aninsulating substrate 41 and an opposing substrate 13 spaced away fromthe insulating substrate 41. A space between the substrates 41 and 13 isfilled with liquid crystal 10. A color filter 12 is disposed on thesubstrate 13, and a transparent common electrode 11 is formed on thecolor filter 12. A gate electrode 9 is formed on the insulatingsubstrate 41, and both the gate electrode 9 and the insulating substrate41 are covered with a gate insulating film 8. A semiconductor layer 7 isformed on the gate insulating film 8 above the gate electrode 9. Asource electrode 4 and a drain electrode 5 are also formed on the gateinsulating film 8 in contact with the semiconductor layer 7. The sourceelectrode 4, the drain electrode 5, the semiconductor layer 7, and thegate electrode 9 cooperate with one another to thereby constitute abottom gate type thin film transistor (hereinafter, "thin filmtransistor" is referred to simply as "TFT").

An interlayer insulating film 42 is formed covering the source electrode4, the drain electrode 5, the semiconductor layer 7, and the gateinsulating film 8 therewith. A contact hole 44 is formed throughout theinterlayer insulating film 42. A pixel electrode 43 made of aluminum isformed on both the interlayer insulating film 42 and an inner sidewallof the contact hole 44.

The drain electrode 5 of TFT is in contact with the pixel electrode 43through the interlayer insulating film 42. As illustrated, theinterlayer insulating layer 42 is designed to have a roughened surfaceby which the pixel electrode 43 acts as a reflection plate for diffusinglights therearound. Lights having been reflected from the pixelelectrode 43 transmit through or are absorbed in the guest-host typeliquid crystal layer 10.

The reflection type liquid crystal display illustrated in FIG. 1remarkable enhances an efficiency of using lights by virtue that apolarizing plate is no longer necessary to be provided, and that thepixel electrode 43 acts as a light reflection plate.

What is important in the illustrated reflection type liquid crystaldisplay is that the pixel electrode 43 as a light reflection plate isdesigned to have a roughened surface. If the pixel electrode 43 weredesigned to have a flat reflection surface, reflected lights would havemore intense orientation, which causes an angle suitable for viewing adisplay (hereinafter, such an angle is referred to as "angle ofvisibility") to become narrower, and which in addition causes scenery toreflect at the pixel electrode 43 as it is like a plane mirror. As aresult, there is caused a problem that a display cannot be seen well.

Thus, it is important that a light-reflection surface is roughened ordesigned to have projections and recesses to thereby uniformly scatterlights therearound. However, if the interlayer insulating layer 42 weredesigned to have projections and recesses to thereby provide the pixelelectrode 43 with a plate for scattering and diffusing lights assuggested in the above-mentioned reflection type liquid crystal displayillustrated in FIG. 1, it would be unavoidable for fabrication steps tobecome complicated, and as a result there would be caused a problem ofan increase in fabrication costs.

In the above-mentioned reflection type liquid crystal display, theinterlayer insulating film 42 is designed to have projections andrecesses by photolithography. However, it is quite difficult to form andcontrol a fine shape of the projections and recesses in micrometer orderby photolithography, and hence the projections and recesses tend tobecome a trapezoid. In addition, there is another problem that it is notpossible to have a uniform characteristic of reflection and scattering.

The reflection type liquid crystal display illustrated in FIG. 1 furtherhas problems as follows. Firstly, it is quite difficult to form thecontact hole 44 connecting the drain electrode 5 to the pixel electrode43 through the interlayer insulating film 42. Secondly, at least sixphotolithography steps have to be carried out in order to form theactive matrix substrate 41 on which TFT, the pixel electrodes 43 and soon are formed. In other words, six different masks are necessary toprepare, and exposure, development and etching steps have to be carriedout six times, both of which causes an increase in a fabrication costand a reduction in a fabrication yield. In addition, errors inregistration between masks and the substrate have to be taken intoaccount. As a result, it is quite difficult to form an active matrixsubstrate larger in size.

In order to solve the above-mentioned problems, Japanese UnexaminedPatent Publication No. 4-338721 has suggested a reflection film made ofa multi-layered dielectric film, for instance. The suggested reflectionfilm brings an advantage that an efficiency of using lights can beenhanced by controlling reflectance of a mirror composed of themulti-layered dielectric film. However, since the mirror composed of themulti-layered dielectric film, acting as a light reflection plate, has apoor characteristic of light scattering, reflected lights have intenseorientation, and accordingly a broader angle of visibility cannot beobtained.

Japanese Unexamined Patent Publication No. 7-306404 has suggested aliquid crystal display having a light diffusion film formed on a topsurface of a transparent pixel electrode, and a plane reflection platedisposed at the rear of the transparent pixel electrode. However, in thesuggested liquid crystal display, lights externally transmitted arescattered by the light reflection film formed on a top surface of thepixel electrode, before the lights are introduced into a liquid crystallayer. Hence, the suggested liquid crystal display cannot sufficientlyprovide display function utilizing birefringence of liquid crystal. Inaddition, a photolithography step has to be carried out seven times forfabricating the liquid crystal display, which causes problems of anincrease in a fabrication cost and a reduction in a fabrication yield.It would be difficult to form a substrate larger in accordance with thesuggested liquid crystal display.

As discussed above, the conventional liquid crystal displays have manyproblems. An advantageous process for readily fabricating a reflectionsurface having projections and recesses is to roughen an insulatingsubstrate, namely, to use so-called ground glass. A reflection surfacehaving projections and recesses could be readily fabricated, forinstance, by forming an aluminum film on a roughened insulatingsubstrate. However, if the reflection surface were fabricated in such amanner, a thin film transistor has to be fabricated on projections andrecesses, as described in Japanese Unexamined Patent Publication No.59-100488. Accordingly, halation tends to readily take place when areflection plate is exposed to lights in a photolithography step, whichwould cause a problem of a design rule being restricted. In addition,there is another problem that the projections and recesses would causedeterioration in transistor performances and reduction in a fabricationyield.

As a solution to those problems, the Japanese Unexamined PatentPublication No. 59-100488 has also suggested that, in a substrate, anarea on which TFT is to be formed remains flat, and only an area onwhich a pixel electrode is to be formed is formed to have projectionsand recesses. However, this is not an appropriate solution, because aquite complicated photo-etching step has to be carried out for remainingthe first mentioned area flat. In addition, at least sevenphotolithography steps have to be carried out for fabricating an activematrix substrate, causing the problems as mentioned earlier. That is, afabrication cost would be increased, and it would be difficult to formthe active matrix substrate larger in size.

As mentioned above, the prior art has to carry out a complicatedphoto-etching step for fabricating projections and recesses at a surfaceof a substrate to thereby have a reflection plate having sufficientlight diffusion performance, which would cause a problem of an increasedfabrication cost. In addition, it would be quite difficult to control areflection characteristic of the reflection plate.

Furthermore, a photolithography step has to be carried out at least sixtimes for fabricating an active matrix substrate including a thin filmtransistor and a reflection plate. Hence, at least six different maskshave to be prepared, and exposure and development steps have to becarried out at least six times. This causes an increase in a fabricationcost and a reduction in a fabrication yield. In addition, errors inregistration between masks and a substrate have to be taken intoaccount, resulting in that it is quite difficult to form an activematrix substrate larger in size.

SUMMARY OF THE INVENTION

In view of the foregoing problems of the prior art, it is an object ofthe present invention to provide a reflection type liquid crystaldisplay which includes a light diffusion and reflection plate havingprojections and recesses formed at a surface thereof and also havingexcellent reflection characteristic.

Another object of the present invention is to provide a reflection typeliquid crystal display which is capable of reducing the number ofphotolithography steps required for fabricating an active matrixsubstrate including a thin film transistor, and hence which can befabricated at lower costs at a higher fabrication yield.

In one aspect of the invention, there is provided a reflection typeliquid crystal display including (a) a first substrate having aroughened surface, (b) a second substrate spaced away from the firstsubstrate in opposing relation to the roughened surface of the firstsubstrate, (c) a liquid crystal layer sandwiched between the first andsecond substrates, (d) a metal film formed on the roughened surface ofthe first substrate for reflecting lights therefrom, (e) a transparentdielectric film formed on the metal film, the transparent dielectricfilm having a planarized upper surface, and (f) at least one transparentpixel electrode formed on the transparent dielectric film.

It is preferable that projections and recesses formed at the roughenedsurface have a difference in height in the range of 0.1 μm to 5 μm bothinclusive. It is also preferable that the projections and recesses areformed at a pitch in the range of 0.5 μm to 50 μm both inclusive. It isfurther preferable that the projections and recesses are formed to havea curved surface or are shaped in wave-form.

For instance, the transparent dielectric film may be made of polyimidefamily resin. The first substrate may be a glass substrate, forinstance. The second substrate may include a transparent insulatingsubstrate, a color filter disposed on the transparent insulatingsubstrate, a transparent, electrically conductive film formed on thecolor filter, and an orientation film formed on the electricallyconductive film.

There is further provided a reflection type liquid crystal displayincluding (a) a first substrate having a roughened surface, (b) a secondsubstrate spaced away from the first substrate in opposing relation tothe roughened surface of the first substrate, (c) a liquid crystal layersandwiched between the first and second substrates, (d) a metal filmformed on the roughened surface of the first substrate for reflectinglights therefrom, (e) a transparent dielectric film formed on the metalfilm, the transparent dielectric film having a planarized upper surface,(f) a plurality of transparent pixel electrodes formed on thetransparent dielectric film, and (g) a plurality of switching devicesformed on the transparent dielectric film, each of the switching devicesbeing electrically connected with each of the transparent pixelelectrodes, the transparent pixel electrodes and the switching devicesbeing arranged in a matrix.

It is preferable that the metal film is formed partially on theroughened surface of the first substrate. For instance, the metal filmmay be formed almost only below the transparent pixel electrodes. As analternative, the metal film may be formed on the roughened surface ofthe first substrate so that the metal film does not exist below theswitching devices.

There is still further provided a reflection type liquid crystal displayincluding (a) a first substrate having a roughened surface, (b) a secondsubstrate spaced away from the first substrate in opposing relation tothe roughened surface of the first substrate, (c) a liquid crystal layersandwiched between the first and second substrates, (d) a metal filmformed on the roughened surface of the first substrate for reflectinglights therefrom, (e) a transparent dielectric film formed on the metalfilm, the transparent dielectric film having a planarized upper surface,(f) a plurality of transparent pixel electrodes formed on thetransparent dielectric film, (g) a plurality of switching devices formedon the transparent dielectric film, each of the switching devices beingelectrically connected with each of the transparent pixel electrodes,the transparent pixel electrodes and the switching devices beingarranged in a matrix, and (h) a film sandwiched between the transparentdielectric film and the switching devices for preventing the switchingdevices from making direct contact with the transparent dielectric film.

The inorganic film may be made of silicon compound such as silicondioxide and silicon nitride. It is preferable that the inorganic filmhas a thickness in the range of 0.03 μm to 0.2 μm both inclusive.

In another aspect of the invention, there is provided a method offabricating a substrate for a reflection type liquid crystal display,including the steps of (a) roughening a surface of a substrate, (b)forming a metal film on the thus roughened surface of the substrate forreflecting lights therefrom, (c) forming a transparent dielectric filmon the metal film so that the transparent dielectric film has aplanarized upper surface, and (d) forming at least one transparent pixelelectrode on the transparent dielectric film.

It is preferable that the first step (a) includes the steps of (a-1)mechanically polishing a surface of the substrate, and (a-2) treatingthe thus mechanically polished surface with chemicals for smoothingsharpened portions thereof. Garnet is preferable used for mechanicallypolishing a surface of the substrate in the step (a-1). A surface of thesubstrate may be mechanically polished by being rubbed with sand in thestep (a-1). As an alternative, a surface of the substrate may bemechanically polished by means of sand blasting in the step (a-1). Aschemicals used in the step (a-2), there may be used hydrofluoric acid orbuffered hydrogen fluoride.

It is preferable that the metal film is formed on the roughened surfaceof the substrate by sputtering in the step (b). For instance, thetransparent dielectric film may be formed by spin-coating polymer on themetal film, in which case, the transparent dielectric film may be formedby the steps of applying liquid prepolymer on the metal film, spreadingthe prepolymer on the metal film so that the prepolymer has an almostuniform thickness, and curing the prepolymer.

The polymer may be selected from at least one of polyamide, polyimide,polyester, acrylic resin, epoxy resin, silicone resin, and polysilazane.

There is further provided a method of fabricating a substrate for areflection type liquid crystal display, including the steps of (a)roughening a surface of a substrate, (b) forming a metal film on thethus roughened surface of the substrate for reflecting lights therefrom,(c) forming a transparent dielectric film on the metal film so that thetransparent dielectric film has a planarized upper surface, (d) forminga plurality of transparent pixel electrodes on the transparentdielectric film, and (e) forming a plurality of switching devices on thetransparent dielectric film so that each of the switching devices iselectrically connected with each of the transparent pixel electrodes,and that the transparent pixel electrodes and the switching devices arearranged in a matrix.

For instance, the step (e) further includes the steps of (e-1) forming atransparent, electrically conductive film on the transparent dielectricfilm, (e-2) patterning the transparent, electrically conductive filminto pixel source, and drain electrodes, (e-3) forming a semiconductorfilm, a gate insulating film, and a metal film over the thus patternedelectrically conductive film and the transparent dielectric film, and(e-4) patterning the thus formed films into gate electrodes.

It is preferable that the metal film is formed partially on theroughened surface of the first substrate in the step (a). For instance,the metal film may be formed almost only below the transparent pixelelectrodes. As an alternative, the metal film may be formed on theroughened surface of the first substrate so that the metal film does notexist below the switching devices, for instance, by removing unnecessaryportions of the metal film by photolithography and etching.

There is still further provided a method of fabricating a substrate fora reflection type liquid crystal display, including the steps of (a)roughening a surface of a substrate, (b) forming a metal film on thethus roughened surface of the substrate for reflecting lights therefrom,(c) forming a transparent dielectric film on the metal film so that thetransparent dielectric film has a planarized upper surface, (d) forminga film on the transparent dielectric film, (e) forming a plurality oftransparent pixel electrodes on the inorganic film, and (f) forming aplurality of switching devices on the inorganic film so that each of theswitching devices is electrically connected with each of the transparentpixel electrodes, and that the transparent pixel electrodes and theswitching devices are arranged in a matrix.

For instance, the film may be an inorganic film, and may be formed tohave a thickness in the range of 0.03 μm to 0.2 μm both inclusive.

In accordance with the invention, a substrate having projections andrecesses and acting as a light diffusion and reflection plate can befabricated by simple steps such as mechanically polishing a surface ofinsulating material such as glass, treating the thus polished glass withchemicals such as hydrogen fluoride, and forming a metal film on thethus treated surface of glass. In addition, it is possible to controlshapes of the projections and recesses by varying conditions forpolishing and treating with chemicals, and hence it is also possible tocontrol an angle of visibility and reflectance of a liquid crystaldisplay.

Even if a substrate is formed to have projections and recesses, it wouldbe possible to form a thin film transistor on the substrate, forinstance, by planarizing a surface of the substrate by spin-coatingpolyimide resin.

In addition, in accordance with the above-mentioned invention, it ispossible to fabricate an active matrix substrate by carrying outphotolithography steps two or three times. Thus, the number of masks andthe number of fabrication steps can be significantly reduced, whichensures that a fabrication cost is reduced and a fabrication yield isenhanced. Since errors in registration between masks and a substrate canbe reduced, a problem that a design rule is restricted can be solved,which ensures that a substrate can be formed larger in size.

The above and other objects and advantageous features of the presentinvention will be made apparent from the following description made withreference to the accompanying drawings, in which like referencecharacters designate the same or similar parts throughout the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a conventional reflection typeliquid crystal display.

FIG. 2 is a partial plane view of an active matrix substrate for areflection type liquid crystal display in accordance with the firstembodiment of the invention.

FIG. 3 is a cross-sectional view taken along the line A--A in FIG. 2.

FIG. 4 is an enlarged cross-sectional view of the substrate of thereflection type liquid crystal display in accordance with the firstembodiment.

FIG. 5 is a partial plane view of a reflection type liquid crystaldisplay in accordance with the second embodiment of the invention.

FIG. 6 is a partial plane view of a reflection type liquid crystaldisplay in accordance with the third embodiment of the invention.

FIG. 7 is a partial plane view of a passive matrix substrate for areflection type liquid crystal display in accordance with the fourthembodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a reflection type liquid crystal display in accordance with theinvention, a pair of insulating substrates such as a glass substrate aredisposed in opposing relation with a liquid crystal layer sandwichedtherebetween. A light transmitted through an upper substrate isreflected and diffused by a light diffusion and reflection plate formedon a lower substrate to thereby make a display. Herein, the lightdiffusion and reflection plate is formed of a substrate havingprojections and recesses at a surface thereof, and a metal film such asan aluminum film, for instance. A transparent dielectric film having aplanarized surface is formed on the substrate having projections andrecesses, and a switching device such as a thin film transistor isfabricated. Thus, a reflection type liquid crystal display having anactive matrix type substrate can be formed in a simpler structure.

The invention may be applied to a reflection type liquid crystal displayhaving a passive matrix type substrate. In this passive matrix typeliquid crystal display, a transparent dielectric film is formed byspin-coating on a light diffusion and reflection plate havingprojections and recesses, and there is not formed a switching device onthe transparent dielectric film. The liquid crystal display works independence on variation in an effective voltage applied to liquidcrystal. By forming the transparent dielectric film thick byspin-coating, a parasitic capacity between a light diffusion andreflection plate and a wiring or a pixel electrode can be decreased.

[Embodiment 1]

FIG. 2 illustrates an active matrix substrate for a reflection typeliquid crystal display in accordance with the first embodiment, and FIG.3 is a cross-sectional view taken along the line A--A in FIG. 2.

As illustrated in FIG. 3, an active matrix substrate in the instantembodiment includes an insulating substrate 1 having an upper surfaceroughened or having projections and recesses, a metal film 2 formed allover the insulating substrate 1 and made of metal such as aluminum,silver, gold and copper, a transparent dielectric film 3 formed all overthe metal film 2, made of polyimide family resin, and designed to have aplanarized surface, a plurality of transparent pixel electrodes 6 formedon the transparent dielectric film 3 and made of ITO (indium-tin-oxide),a thin film transistor (hereinafter, referred to simply as "TFT") 20formed on the transparent dielectric film 3, and an orientation film(not illustrated) formed over the active matrix type substrate andtreated for orienting liquid crystal molecules.

As illustrated in FIG. 2, there are formed a plurality of gate buswirings 21 and a plurality of source bus wirings 22 on the active matrixsubstrate. The gate bus wirings 21 are made of chromium, tantalum,molybdenum or aluminum, and arranged in parallel with one another. Thesource bus wirings 22 are made of ITO, and arranged in parallel with oneanother and perpendicularly to the gate bus wirings 21. A thin filmtransistor (TFT) 20 is formed as a switching device at each ofintersections of the gate bus wirings 21 and the source bus wirings 22.A portion 9 extending from each of the gate bus wirings 21 constitutes agate electrode of TFT 20, and a portion 4 extending from each of thesource bus wirings 22 constitutes a source electrode of TFT 20. Asillustrated in FIG. 3, each of the drain electrodes 5 of TFT 20 is inconnection with the each of the transparent pixel electrodes 6.

TFT 20 has the following structure. A source electrode 4 and a drainelectrode 5 both made of a transparent, electrically conductive filmsuch as an ITO film are formed on the transparent dielectric film 3. Thedrain electrode 5 is in connection with the pixel electrode 6. On thesource and drain electrodes 4 and 5 is formed an amorphous siliconsemiconductor layer 7 so that it is in connection with both the sourceand drain electrodes 4 and 5. A gate insulating film 8 made of siliconnitride is formed on the semiconductor layer 7, and a gate electrode 9made of metal such as chromium, tantalum, molybdenum and aluminum isformed on the gate insulating film 8.

A substrate disposed in opposing relation to the active matrix substrateincludes a transparent insulating substrate 13 made of glass, a colorfilter 12 formed on the substrate 13, a common electrode 11 made of atransparent, electrically conductive film such as an ITO film and formedon the color filter 12, and an orientation film (not illustrated) formedon the common electrode 11.

The reflection type liquid crystal display having the above-mentionedstructure is fabricated as follows.

First, a surface of a glass substrate is mechanically roughened. Forinstance, a glass substrate is rubbed with sand at a surface thereof.Rubbing with sand is generally used for fabricating a flat glass.However, even if a glass substrate is mechanically polished by beingrubbed with sand, a difference in height between a bottom of a recessand a summit of a projection, and a pitch between summits of adjacentprojections become merely about 0.1 μm. Thus, garnet powder is employedfor polishing a substrate in the instant embodiment to thereby obtainthe difference in height in the range of 1 μm to 2 μm both inclusive,and the pitch in the range of 5 μm to 15 μm. Herein, garnet is silicatemineral of aluminum, iron and so on. Herein, with reference to FIG. 4, adifference in height between a bottom of a recess and a summit of aprojection is defined as a height "h", and a pitch between summits ofadjacent projections is defined as a length "p".

Then, the thus roughened glass substrate is immerged into liquidchemicals such as hydrofluoric acid and buffered hydrogen fluoride.Since the roughened surface of the glass substrate has sharpenedprojections and recesses by mechanical polishing, they are smoothed bytreatment with chemicals for the purpose of enhancing coverage of themetal film 2 to be later formed on the glass substrate and uniformizinglight diffusion of the metal film 2. The difference in height between abottom of a recess and a summit of a projection varies in dependence ofspecific chemicals and/or time during which the glass substrate isimmerged into chemicals. In the instant embodiment, the difference inheight in the range of 1 μm to 2 μm is made to change into a differencein height in the range of 0.4 μm to 1.2 μm by immerging the substrateinto 10% hydrofluoric acid by five minutes.

By the above-mentioned simple steps, the glass substrate is designed tohave a smoothly roughened surface having projections and recesses adifference in height of which is in the range of 0.4 μm to 1.2 μm, and apitch of which is in the range of 5 μm to 15 μm.

Then, aluminum, silver, gold, copper or alloy mainly containing them isdeposited on the glass substrate by sputtering to thereby form a metalfilm having high reflectance by a thickness in the range of 0.1 μm to 1μm. The thus formed metal film acts as a light diffusion and reflectionplate 2.

Then, a transparent dielectric film 3 made of polyimide family resin isformed on the metal film 2 by spin-coating by a thickness in the rangeof 2 μm to 5 μm to thereby planarize the roughened surface of the glasssubstrate 1. Specifically, viscous liquid prepolymer is applied onto themetal film 2, and then is spread by means of a spin-coater so that theprepolymer has almost uniform thickness all over the glass substrate 1.Then, the glass substrate 1 is kept in a kiln at 250° C. for 30 minutes,for instance, to thereby cure the prepolymer. Thus, there is formed thetransparent dielectric film 3 having a planarized surface.

Then, a transparent, electrically conductive film made of ITO is formedover the transparent dielectric film 3 by sputtering by a thickness inthe range of 0.01 μm to 0.3 μm. Then, the thus formed electricallyconductive film is patterned by photolithography and dry etching tothereby form the source bus wirings 22, the source electrode 4, thedrain electrode 5, and the pixel electrode 6.

After the substrate 1 has been subject to plasma treatment in phosphinegas, an amorphous silicon layer, which will make the semiconductor layer7, is formed over the source electrode 4, the transparent dielectricfilm 3 and the drain electrode 5 by plasma-enhanced chemical vapordeposition (hereinafter, "chemical vapor deposition" is referred tosimply as "CVD") by a thickness in the range of 0.03 μm to 0.3 μm, asilicon nitride or silicon dioxide film, which will make the gateinsulating film 8, is formed over the amorphous silicon layer byplasma-enhanced CVD by a thickness in the range of 0.2 μm to 0.6 μm, anda metal film made of metal such as chromium, tantalum, molybdenum andaluminum, which will make the gate electrode 9, is formed over thesilicon nitride or silicon dioxide film by sputtering by a thickness inthe range of 0.1 μm to 0.5 μm.

Then, the metal film is patterned into a desired pattern byphotolithography and dry etching to thereby form the gate electrode 9and the gate bus wirings 21. Subsequently, the silicon nitride orsilicon oxide film and the amorphous silicon layer are patterned byetching either by employing the photoresist mask common to the mask usedfor patterning the gate electrode 9 or by employing the thus patternedmetal film from which a photoresist layer is removed, as a mask, tothereby form the gate insulating film 8 and the semiconductor layer 7.Thus, there is completed the active matrix substrate.

As mentioned above, the active matrix substrate in accordance with theinstant embodiment can be fabricated by carrying out photolithographysteps only twice.

On the other hand, the opposing substrate is fabricated by forming thecolor filter 12 on the glass substrate 13, and then forming an ITO filmon the color filter 12 by sputtering as the transparent common electrode11. The color filter 12 includes a light-impermeable portion and coloredportions including red, green and blue portions.

Then, orientation films (not illustrated) are applied onto both thetransparent common electrode 11 of the substrate 13, and TFT 20 and thepixel electrode 6 of the substrate 1. Then, the substrates 1 and 13 aredisposed in facing relation with 3-8 μm-diameter plastic ballsinterposed therebetween so that the orientation films face each other,and are adhered to each other with sealing resin. Thereafter, liquidcrystal material is introduced through an opening having been in advanceformed at a certain location of the sealing resin, and then the openingis closed. The liquid crystal material contains two or more kinds ofdichroism pigments and optically active substance having chirality.Thus, there is obtained a guest-host mode reflection type liquid crystaldisplay.

The guest-host mode utilizes a phenomenon that when pigments, which arebar-shaped molecules having dichroism, are introduced into liquidcrystal, the pigments are oriented in accordance with liquid crystalmolecules to a high degree. More specifically, the guest-host mode isbased on a principle that pigment molecules stand when liquid crystalmolecules stand relative to an incident plane through which a light istransmitted, in which case a light transmits through a liquid crystallayer, whereas pigment molecules lie when liquid crystal molecules lierelative to an incident plane through which a light is transmitted, inwhich case a light is absorbed into pigments and cannot transmit througha liquid crystal layer. The guest-host mode can be applied to an opticalswitching device. It would be possible to absorb all lights having awavelength belonging to a visible range by adding two or more kinds ofdichroism pigments into liquid crystal.

The guest-host mode makes it no longer necessary to use a polarizingplate which was necessary to use in a conventional twist nematic typeliquid crystal display. Thus, a problem that only one polarizationelement of a light can be utilized by a polarizing plate can be solved,and as a result, a light efficiency can be significantly enhanced.

In the above-mentioned first embodiment, the roughened surface of thesubstrate 1 has the projections and recesses defined by the difference"h" in height in the range of 0.4 μm to 1.2 μm and the pitch "p" in therange of 5 μm to 15 μm. According to the results of the experiments theinventors had conducted, when the difference "h" in height is in therange of 0.1 μm to 5 μm both inclusive and the pitch "p" is in the rangeof 0.5 μm to 50 μm both inclusive, optically excellent projections andrecesses are obtained.

It should be noted that the insulating substrate 1 may be roughened bysand-blast where fine particles are intensively blown onto a surface ofa substrate to thereby form desired projections and recesses, in placeof by being rubbed with sand.

In addition, the transparent dielectric film 3 may be made of polymersuch as polyamide, polyester, acrylic resin, epoxy resin, siliconeresin, and polysilazane, or of material mainly containing them, as wellas of polyimide family resin.

[Embodiment 2]

FIG. 5 illustrates a reflection type liquid crystal display inaccordance with the second embodiment. The second embodiment has almostthe same structure as that of the first embodiment, but is differentfrom the first embodiment only in that the metal film or light diffusionand reflection film 2 is formed only below the transparent pixelelectrode 6, and that the metal film 2 except a region below thetransparent pixel electrode 6 is removed.

If the transparent pixel electrode 6 were formed under TFT 20 like thefirst embodiment, a light reflected at the light diffusion andreflection plate 2 tends to enter the semiconductor layer 7, asindicated with broken lines B. If a light would enter the semiconductorlayer 7, an off-resistance in the semiconductor layer 7 is decreased,and accordingly a leakage current is increased with the result thatdisplay grade is deteriorated. Hence, in the second embodiment, aportion of the light diffusion and reflection light 2 located under thesemiconductor layer 7 is removed to thereby significantly reduce a lightfrom entering the semiconductor layer 7. Namely, a light reflected atthe light diffusion and reflection plate 2 is not directed to thesemiconductor layer 7, as indicated with a solid line A.

The reflection type liquid crystal display in accordance with the secondembodiment is fabricated as follows. First, the glass substrate 1 isroughened similarly to the first embodiment 1, and then a metal film isdeposited on the thus roughened glass substrate 1 by sputtering. Then,unnecessary portions of the metal film are removed by photolithographyand etching to thereby the light diffusion and reflection plate 2disposed only below the pixel electrode 6. The subsequent steps are thesame as those of the first embodiment. Thus, there is obtained thereflection type liquid crystal display in accordance with the secondembodiment.

In accordance with the second embodiment, the active matrix substratecan be fabricated by carrying out photolithography steps three times.

[Embodiment 3]

A reflection type liquid crystal display in accordance with the thirdembodiment is almost the same as the first embodiment, but is differentonly in that an inorganic film 45 is formed on the transparentdielectric film 3. The pixel electrodes 6 and TFT 20 are formed on theinorganic film 45 similarly to the first embodiment.

In the reflection type liquid crystal display in accordance with thefirst embodiment, the transparent dielectric film 3 makes direct contactwith the semiconductor layer 7. Hence, there may be caused a problemthat an interface level at an interface between the transparentdielectric film 3 and the semiconductor layer 7 may be increased, andthat the semiconductor layer 7 may absorb impurities contained in thetransparent dielectric film 3 to thereby deteriorate performances of athin film transistor, in dependence on material of which the transparentdielectric film 3 is made. It is possible to avoid the semiconductorlayer 7 from making direct contact with the transparent dielectric film3 by forming the inorganic film 45 between the transparent dielectricfilm 3 and the semiconductor layer 7.

The inorganic film 45 may be made of material often employed as aninsulator in the field of fabrication of a semiconductor device. Forinstance, the inorganic film 45 is made of silicon dioxide and siliconnitride. In the instant embodiment, the inorganic film 45 is designed tohave a thickness in the range of 0.03 μm to 0.2 μm.

[Embodiment 4]

The invention may be applied to a passive matrix type liquid crystaldisplay. The fourth embodiment relates to a passive matrix type liquidcrystal display to which the invention is applied. FIG. 7 illustrates aliquid crystal display in accordance with the fourth embodiment.

A passive matrix type liquid crystal display makes a display independence only on variation in an effective voltage applied to liquidcrystal without using a switching device as TFT. As illustrated in FIG.7, a reflection type liquid crystal display in accordance with thefourth embodiment does not include TFT.

As illustrated in FIG. 7, a passive matrix substrate in the instantembodiment includes an insulating substrate 1 having an upper surfaceroughened or having projections and recesses, a metal film 2 formed allover the insulating substrate 1 and made of metal such as aluminum,silver, gold and copper, a transparent dielectric film 3 formed all overthe metal film 2, made of polyimide family resin, and designed to have aplanarized surface, a plurality of column electrodes 46 formed on thetransparent dielectric film 3, and an orientation film (not illustrated)formed over the column electrodes 46 and treated for orienting liquidcrystal molecules.

A substrate disposed in opposing relation to the passive matrixsubstrate includes a transparent insulating substrate 13 made of glass,a color filter 12 formed on the substrate 13, a plurality of rowelectrodes 47 formed on the color filter 12, and extending in adirection perpendicular to a direction in which the column electrodes 46extend, and an orientation film (not illustrated) formed on the rowelectrode 47.

The substrates 1 and 13 are disposed in facing relation so that theorientation films face each other, and are adhered to each other withsealing resin. A space between the substrates 1 and 13 are filled withthe liquid crystal layer 10.

The column electrodes 46 and the row electrodes 47 cooperate with eachother to thereby control a voltage applied to the liquid crystal layer10. Since the column electrodes 46 and the row electrodes 47 act notonly as wirings, but also as pixel electrodes, they are made of ITOwhich is transparent, electrically conductive material.

Since a passive matrix type liquid crystal display makes a liquidcrystal display by varying an effective voltage, if too much parasiticcapacity were coupled to the column electrodes 46, driving pulses toapply to the row electrodes 47 are distorted with the result ofsignificant deterioration in display quality. Hence, the transparentdielectric film 3 in the instant embodiment is formed thick byspin-coating for reducing a parasitic capacity between the columnelectrodes 46 and the metal film 2. The transparent dielectric film 3 isdesigned to have a thickness of 5 μm in the instant embodiment. Thetransparent dielectric film 3 may have a greater thickness. Since thetransparent dielectric film 3 is designed to have a planarizing uppersurface, there is no fear that the column electrodes 46 formed on thetransparent dielectric film 3 are broken by the projections and recessesof the roughened surface of the substrate 1.

While the present invention have been described in connection with thepreferred embodiments, in accordance with the present invention, it ispossible to form projections and recesses by simple steps to therebyobtain a light diffusion and reflection plate having suitable reflectionproperty. In addition, the transparent dielectric film formed on theroughened surface of the substrate and having a planarized upper surfacemakes it possible to make an active matrix substrate by carrying outphotolithography steps only two or three times, which is smaller in thenumber of carrying out photolithography steps than the conventionalmethod of fabricating an active matrix substrate.

Hence, the present invention provides a reflection type liquid crystaldisplay having high display grade and high reliability at a low cost andat a high fabrication yield. In addition, since a design rule for TFT isno longer restricted, a reflection type liquid crystal display can befabricated in a greater size with higher density.

Furthermore, the present invention provides a reflection type liquidcrystal display having a sufficiently high light efficiency, because areflection plate is incorporated in an active matrix substrate, and itis no longer necessary to use a polarizing plate by utilizing theguest-host mode.

The present invention may be applied to a passive matrix type liquidcrystal display.

While the present invention has been described in connection withcertain preferred embodiments, it is to be understood that the subjectmatter encompassed by way of the present invention is not to be limitedto those specific embodiments. On the contrary, it is intended for thesubject matter of the invention to include all alternatives,modifications and equivalents as can be included within the spirit andscope of the following claims.

The entire disclosure of Japanese Patent Application No. 8-292408 filedon Nov. 5, 1996 including specification, claims, drawings and summary isincorporated herein by reference in its entirety.

What is claimed is:
 1. A method of fabricating a substrate for areflection type liquid crystal display, comprising the steps of:(a)roughening a surface of a substrate; (b) forming a metal film on thethus roughened surface of said substrate for reflecting lightstherefrom; (c) forming a non-polarizing, transparent dielectric film onsaid metal film so that said transparent dielectric film has aplanarized upper surface; and (d) forming at least one transparent pixelelectrode on said transparent dielectric film; wherein said transparentdielectric film is formed by spin-coating polymer on said metal film. 2.The method as set forth in claim 1, wherein said transparent dielectricfilm is formed by the steps of:(a) applying liquid prepolymer on saidmetal film; (b) spreading said prepolymer on said metal film so thatsaid prepolymer has an almost uniform thickness; and (c) curing saidprepolymer.
 3. The method as set forth in claim 1, wherein said polymerincludes at least one of polyamide, polyimide, polyester, acrylic resin,epoxy resin, silicone resin, and polysilazane.
 4. A method offabricating a substrate for a reflection type liquid crystal display,comprising the steps of:(a) roughening a surface of a substrate; (b)forming a metal film on the thus roughened surface of said substrate forreflecting lights therefrom; (c) forming a non-polarizing, transparentdielectric film on said metal film so that said transparent dielectricfilm has a planarized upper surface; (d) forming a plurality oftransparent pixel electrodes on said transparent dielectric film; and(e) forming a plurality of switching devices on said transparentdielectric film so that each of said switching devices is electricallyconnected with each of said transparent pixel electrodes, and that saidtransparent pixel electrodes and said switching devices are arranged ina matrix; wherein said transparent dielectric film is formed byspin-coating polymer on said metal film.
 5. The method as set forth inclaim 4, wherein said transparent dielectric film is formed by the stepsof:(a) applying liquid prepolymer on said metal film; (b) spreading saidprepolymer on said metal film so that said prepolymer has an almostuniform thickness; and (c) curing said prepolymer.
 6. The method as setforth in claim 4, wherein said polymer includes at least one ofpolyamide, polyimide, polyester, acrylic resin, epoxy resin, siliconeresin, and polysilazane.
 7. A method of fabricating a substrate for areflection type liquid crystal display, comprising the steps of:(a)roughening a surface of a substrate; (b) forming a metal film on thethus roughened surface of said substrate for reflecting lightstherefrom; (c) forming a non-polarizing, transparent dielectric film onsaid metal film so that said transparent dielectric film has aplanarized upper surface; (d) forming a plurality of transparent pixelelectrodes on said transparent dielectric film; and (e) forming aplurality of switching devices on said transparent dielectric film sothat each of said switching devices is electrically connected with eachof said transparent pixel electrodes, and that said transparent pixelelectrodes and said switching devices are arranged in a matrix; whereinsaid surface is roughened in said step (a) so that there are formedprojections and recesses having a difference in height in the range of0.1 μm to 5 μm both inclusive.
 8. A method of fabricating a substratefor a reflection type liquid crystal display, comprising the stepsof:(a) roughening a surface of a substrate; (b) forming a metal film onthe thus roughened surface of said substrate for reflecting lightstherefrom; (c) forming a non-polarizing, transparent dielectric film onsaid metal film so that said transparent dielectric film has aplanarized upper surface; (d) forming a plurality of transparent pixelelectrodes on said transparent dielectric film; and (e) forming aplurality of switching devices on said transparent dielectric film sothat each of said switching devices is electrically connected with eachof said transparent pixel electrodes, and that said transparent pixelelectrodes and said switching devices are arranged in a matrix; whereinsaid metal film is formed partially on said roughened surface of saidfirst substrate in said step (b).
 9. The method as set forth in claim 8,wherein said metal film is formed almost only below said transparentpixel electrodes.
 10. The method as set forth in claim 8, wherein saidmetal film is formed on said roughened surface of said first substrateso as not to exist below said switching devices.
 11. The method as setforth in claim 8, wherein unnecessary portions of said metal film isremoved by photolithography and etching.
 12. A method of fabricating asubstrate for a reflection type liquid crystal display, comprising thesteps of:(a) roughening a surface of a substrate; (b) forming a metalfilm on the thus roughened surface of said substrate for reflectinglights therefrom; (c) forming a non-polarizing, transparent dielectricfilm on said metal film so that said transparent dielectric film has aplanarized upper surface; (d) forming a film on said transparentdielectric film; (e) forming a plurality of transparent pixel electrodeson said film; and (f) forming a plurality of switching devices on saidfilm so that each of said switching devices is electrically connectedwith each of said transparent pixel electrodes, and that saidtransparent pixel electrodes and said switching devices are arranged ina matrix; wherein said transparent dielectric film is formed byspin-coating polymer on said metal film.
 13. The method as set forth inclaim 12, wherein said transparent dielectric film is formed by thesteps of:(a) applying liquid prepolymer on said metal film; (b)spreading said prepolymer on said metal film so that said prepolymer hasan almost uniform thickness; and (c) curing said prepolymer.
 14. Themethod as set forth in claim 12, wherein said polymer includes at leastone of polyamide, polyimide, polyester, acrylic resin, epoxy resin,silicone resin, and polysilazane.
 15. A method of fabricating asubstrate for a reflection type liquid crystal display, comprising thesteps of:(a) roughening a surface of a substrate; (b) forming a metalfilm on the thus roughened surface of said substrate for reflectinglights therefrom; (c) forming a non-polarizing, transparent dielectricfilm on said metal film so that said transparent dielectric film has aplanarized upper surface; (d) forming a film on said transparentdielectric film; (e) forming a plurality of transparent pixel electrodeson said film; and (f) forming a plurality of switching devices on saidfilm so that each of said switching devices is electrically connectedwith each of said transparent pixel electrodes, and that saidtransparent pixel electrodes and said switching devices are arranged ina matrix; wherein said metal film is formed partially on said roughenedsurface of said first substrate in said step (b).
 16. The method as setforth in claim 15, wherein said metal film is formed almost only belowsaid transparent pixel electrodes.
 17. The method as set forth in claim15, wherein said metal film is formed on said roughened surface of saidfirst substrate so as not to exist below said switching devices.
 18. Themethod as set forth in claim 15, wherein unnecessary portions of saidmetal film is removed by photolithography and etching.